In the context of the invention, the expression "formose" applies to the mixtures known per se of low molecular weight polyhydroxyl compounds (polyhydric alcohols, hydroxy aldehydes and hydroxy ketones) which are formed by the condensation of formaldehyde hydrate.
The production of mixtures of polyhydric alcohols, hydroxy aldehydes and hydroxy ketones by the autocondensation of formaldehyde hydrate is described in numerous literature references. (See e.g. Butlerow and Loew, Annalen 120, 295 (1861) and J. pr. Chem. 33, 321 (1886); Pfeil, chemische Berichte 84, 229 (1951); Pfeil and Schroth, chemische Berichte 85, 303 (1952); R. D. Partridge and A. H. Weiss, Carbohydrate Research 24, 29-44 (1972); the formoses of glycerol aldehyde and dioxy acetone according to Emil Fischer; German Pat. Nos. 882,385; 830,951 and 884,794; U.S. Pat. Nos. 2,224,910; 2,269,935 and 2,272,378 and British Pat. No. 513,708.) However, these conventional processes have certain disadvantages such as toxic catalyst, poor volume-time yields and discoloring secondary products. New processes have recently been developed by which it is possible to produce substantially colorless formoses free from troublesome secondary products in high yields using conventional catalysts.
One of these new processes comprises condensing formaldehyde hydrate in the presence of soluble or insoluble lead(II)salts or lead(II)ions fixed to high molecular weight supports as catalysts and in the presence, as co-catalyst, of a mixture of hydroxy aldehydes and hydroxy ketones such as is formed in the condensation of formaldehyde hydrate and which has the following molar ratios:
Compounds containing 3 carbon atoms/compounds containing 4 carbon atoms: 0.5:1 to 2.0:1 PA0 Compounds containing 4 carbon atoms/compounds containing 5 carbon atoms: 0.2:1 to 2.0:1 PA0 Compounds containing 5 carbon atoms/compounds containing 6 carbon atoms: 0.5:1 to 5.0:1. PA0 (a) 20 to 90% by weight, preferably 40 to 70% by weight, based on (a)+(b), of a mixture of polyhydric alcohols, hydroxy aldehydes and hydroxy ketones which have been obtained by the condensation of formaldehyde hydrate, PA0 (b) 10 to 80% by weight, preferably 25 to 60% by weight, based on (a)+(b), of aldehydes and/or ketones methylolated in the .alpha.-position and incapable of endiol formation, PA0 (c) 0 to 50% by weight, preferably 0.3 to 30% by weight and, with particular preference, 0.8 to 10% by weight, based on (a)+(b) of water and PA0 (d) 0 to 100% by weight, preferably 10 to 50% by weight, based on (a)+(b), of monosaccharides and/or disaccharides. PA0 (a) soluble or insoluble salts of metals of the Second to Fourth Main Group or of the First to Eighth Secondary Group of the Periodic System of Elements or metal ions fixed to a high molecular weight support, PA0 (b) aldehydes and/or ketones capable of .alpha.-aldolation or their .alpha.-methylolation products and, optionally, PA0 (c) co-catalysts based on compounds capable of enediol formation, until the residual formaldehyde content is from 0 to 10% by weight, preferably from 0.5 to 6% by weight, based on the reaction mixture. The catalyst is subsequently removed in known manner and the reaction product concentrated to the required water content. PA0 (a) soluble or insoluble salts of metals of the Second to Fourth Main Group or of the First to Eighth Secondary Group of the Periodic System of Elements or metal ions fixed to a high molecular weight support, and PA0 (b) a co-catalyst based on compounds capable of enediol formation, PA0 (A) polyisocyanates with PA0 (B) polyhydroxyl compounds having a molecular weight of less than 400, optionally PA0 (C) polyhydroxyl compounds having a molecular weight of from 400 to 10,000 and, optionally, other isocyanate-reactive compounds, optionally in the presence of PA0 (D) blowing agents, catalysts, fillers and other additives known per se,
The proportion of components containing from 3 to 6 carbon atoms should be at least 75% by weight and preferably to more than 85% by weight, based on the total co-catalyst.
The reaction temperature is generally held in the range from 70.degree. to 110.degree. C. and preferably in the range from 80.degree. to 100.degree. C. The pH-value of the reaction solution is adjusted by the controlled addition of an inorganic or organic base up to a conversion of from 10 to 60%, preferably from 30 to 50%, to a value of from 6.0 to 8.0 and preferably to a value of from 6.5 to 7.0, and then to a value of from 4.0 to 6.0 and preferably to a value of from 5.0 to 6.0. It has surprisingly been found that the product distribution of the corresponding polyol, hydroxy aldehyde and hydroxy ketone mixtures can be varied reproducibly by this special pH-profile and by subsequent cooling at different residual formaldehyde contents (0 to 10% by weight, preferably 0.5 to 6% by weight).
After the autocondensation of the formaldehyde hydrate has been interrupted by cooling and/or by deactivating the lead-containing catalyst with acids, the catalyst may be removed in known manner and the water present in the products is evaporated. For further particulars, see German Offenlegungsschrift No. 2,639,084.
Another possible method for obtaining highly concentrated colorless formoses in high volume-time yields is to condense aqueous formalin solutions and/or paraformaldehyde dispersions in the presence of a soluble or insoluble metal catalyst and a co-catalyst produced by partial oxidation of a dihydric or polyhydric alcohol containing at least two vicinal hydroxyl groups and having a molecular weight of from 62 to 242 or a mixture of such alcohols. The pH-value of the reaction solution is being kept between 6.0 and 9.0 by the controlled addition of a base up to a conversion of from 5 to 40% and is subsequently adjusted to between 4.5 and 8.0 to terminate the condensation reaction so that the pH-value is then 1.0 to 2.0 units lower than in the first phase of the reaction. The reaction is then interrupted by deactivating the catalyst at a residual formaldehyde content of from 0 to 10% by weight and the catalyst removed. This process is described in detail in German Offenlegungsschrift No. 2,714,084.
High-quality formoses can also be obtained by condensing formaldehyde in the presence of a metal catalyst and more than 10% by weight, based on formaldehyde, of one or more dihydric or polyhydric low molecular weight alcohols and/or relatively high molecular weight polyhydroxyl compounds. Formose-polyol mixtures such as these are the subject of German Offenlegungsschrift No. 2,714,104.
The properties of the formose (i.e. the average hydroxyl functionality, degree of branching and content of reducing groups) may be widely varied, depending upon the manner in which condensation of the formaldehyde is carried out. In general, the average molecular weight and, hence, the hydroxyl functionality of the formoses, increases as the condensation reaction is continued, i.e. as the quantity of residual formaldehyde present when the condensation reaction is terminated is lowered. Thus, if the condensation reaction is continued up to a residual formaldehyde content of from 0 to 1.5% by weight, the formose obtained contains approximately 25% by weight of compounds containing 5 carbon atoms, 45% by weight of compounds containing 6 carbon atoms and approximately 20% by weight of compounds containing 7 or more carbon atoms. By contrast, a total of only about 10% of polyols, hydroxy ketones and hydroxy aldehydes containing 2, 3, and 4 carbon atoms is obtained. This corresponds to an average hydroxyl functionality of approximately 5.
As explained above, other component distributions of the starter mixtures are obtained by terminating autocondensation of the formaldehyde at somewhat higher residual formaldehyde contents. Thus, termination of the condensation reaction at a formaldehyde content of from 2 to 2.5% gives a mixture of polyhydric alcohols, hydroxy aldehydes and hydroxy ketones having an average hydroxyl functionality of approximately 4. Other component distributions having an even more reduced average hydroxyl functionality are obtained by terminating the condensation reaction at residual formaldehyde contents of greater than 2.5.
By mixing the formose with difunctional or more highly functional low molecular weight alcohols, the functionality of the products may be further varied in cases where it is desired to obtain certain specified properties. Suitable low molecular weight polyhydric alcohols of this type having molecular weights of up to about 300 include ethylene glycol, 1,2-propane diol, 1,3-propane diol, 1,4-butane diol, diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol, dibutylene glycol, glycerol, trimethylol propane, pentaerythritol, sorbitol, butane triols and hexane triols and the like as well as ethoxylation products of these alcohols or even hydrogenated formose (formitol).
It is also possible to use amines and/or ethanolamines as a mixing component. Examples include mono-, di- and tri-ethanolamine, mono-, di- and tri-isopropanolamine, N-alkanolamines, such as N-methyl diethanolamine and N-ethyl diethanolamine, and lower aliphatic monoamines and polyamines, such as ethylamine, ethylene diamine, diethylene triamine and triethylene tetraamine.
According to earlier proposals in particular the already mentioned e.g. German Offenlegungsschriften Nos. 2,639,084; 2,714,084 and 2,714,104, formoses may be used as polyol components in the polyisocyanate polyaddition process for the production of polyurethane plastics.